John p



(No Model J. P. MOMAHON.

THERMOSTAT.

N0. 426,304. Patented/Apr. 22, 1890.

UNITED STATES PATENT OEEIcE.

JOHN P. MCMAHON, OF BUFFALO, NET YORK, ASSIGNOR TO THE MCMAHON THERMOGRAPH COMPANY, OF JERSEY CITY, NEW JERSEY.

T H E R M O S TAT SPECIFICATION forming part of Letters Patent No. 426,304, dated .April 22, 1890.

Application tiled October '7, 1889, Serial No. 826,181. (No model.)

To all whom t may concern: has a screw-threaded aperture, into which a Be it known that I, JOHN P. MCMAHON, a citithreaded tube T is screwed. The exposed end Zen of the United States, residing in Buialo, of the ltube is sealed by a thin disk, preferain the county of Erie and State ot' New York, bly of brass, which is soldered to the body of 5 have invented certain new and useful Imthe tube with solder, which fuses at a degree 55 provements in Thermostats, of which the fol of temperature previously determined. The

lowing description, in connection with the acouter end of post P rests against this disk and eompanying drawings, is a specification. its inner end rests against the spring contact- My invention relates to thermostats empiece 2. The pestis reduced in diameter near 1o ployed for automatically breaking the conits inner end, forming a shoulder p. The re- 6o nections of a normally-closed electric circuit duced portion is passed through a hole p in and completing the connections of a normallythe piece 4, in order that the lower end of the open electric circuit when the temperature at post may rest against the piece 2, which under the place where the instrument is placed has lies the piece 4. The shoulder p rests against r 5 risen to a predetermined degree. the piece 4. 65

The object ot the invention is to provide an Vhen the tube T is screwed into the case O, instrument that will respond uniformly when the insulated rod P forces strips l and 2 into subjected to a given amount of heat, will be contact and separates strips 3 and 4, holding free from liability to derangement by dust or them apart, thus completing the normallyzo by shocks, will be reliable under all circum closed circuit and breaking thenormally-open 7o stances, and will be easily repaired. circuit. Then the temperature rises beyond The invention consists in the construction the degree at which the solder fuses, the disk and arrangement of` parts as vhereinafter de- D is freed from tube T, post P is released, scribed and claimed. strips l and 2 separate, thus breaking the 25 In the accompanying drawings, wherein like normally-closed circuit, and strips 3 and 4 75 letters and numerals of reference indicate like contact, thus closing the normally-open cirparts in the several figures, Figure l is a plan cuit. In this manner two distinct signals are View of my improved thermostat. Fig. 2 is a transmitted upon the two circuits in case of similar view of the same with a portion of the ire, and the transmission of false alarms,

3o casing removed. Fig. 3 is a partly-sectional caused by derangement of either circuit, is 8o View of the same, and Fig. 4 is asectional View prevented. on a plane at right angles to the plane of Fig. 3. It will be seen that the strips are held posi- Uponasuitable insulated baseAfour spring tively in their normal position and cannot be metal strips or contact-pieces are secured. caused to make or break contact by shocks 3 5 Strips l and 2 are connected to binding-posts or vibration of the wall or ceiling to which 85 B and B2, to which are attached the terminals the thermostat is secured. As the electrical of the normally-closed circuit. These strips contacts are inclosed in astout and tight case, are in electrical contact when the instrument they are protected from injury by violence is in its normal condition-that is, when closed and from derangement by dust. y It' the ther- 4o ready to send a lire-alarm. They complete mostat has been used, all that is necessary is 9o thecircuit from post B to post B2, and are to unscrewthetubeand replace it withanother. held in contact with each other by the insul claim lated post P. The strips 3 and4 are connected l. The combination of a case, a tube formed to binding-posts B3 and B4, to which are atwith threads to engage said case and to be held 45 tached the terminals of wires forming part of against movement, a disk secured to the tube 95 the normally-open circuit. These strips are with fusible solder, fixed contact-points and separated when the thermostat is closed, but two independent spring` contact-points formcomplete the normallyopen circuit when the ing the terminals of two different electrical thermostat is operated by heat. The strips circuits, and an insulated post adapted to rest 5o are inclosed in a stout metal case O, which against said disk and to engage both of said 10o spring-contacts and hold them against the springepressure, as and for the purpose described.

2. The combination of a case having an aperture, a tube engaging; said case, a disk secured to the tube with fusible solder, an insulated post formed with a shoulder, spring contactfpieces 1 and 2, held in contact by the lower end of said post, and 'spring contactpieces 3 and 4, held out of contact by the shoulder of said post, as and for the purpose described.

3. The combination of a case having a screwthreaded aperture, a threaded tube engaging said aperture, a disk secured to the tube with fusible solder, an insulated post formed with a reduced lower end and a shoulder, spring` contactpieces l and 2, held in contact by the lower end of said post, and spring contact-pieces 3 and 4 overlying` said firstnamed contact-pieces and held out of contact by engagement with the shoulder of said post, as and for the purpose described.

4. The combination of the insulated base A, the case O, having` a screw-threaded aperture, the threaded tube T, engaging said aperture, the disk D, secured to the .tube with fusible solder, the insulated post P, formed with a shoulder, spring contact-pieces l and 2, held in contact by the lower end of said post, and spring contact-pieces 3 and 4, held out of contact by the shoulder on said post, as and for the purpose described.

In witness whereof l affix my signature in presence of two witnesses.

JOHN P. MCMAHON. W'itnesses:

PETER S'ro'r'r, JOHN WrLLIAMsoN. 

